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Dehydrogenases are enzymes that oxidize their substrate by splitting off hydrogen anions (formally H - ) . They should not be confused with the dehydratases, which split off water. Dehydrogenases belong to group I ( oxidoreductases ) of the EC classification , they occupy the two subclasses EC 1.1.1.- and EC 1.1.2.- . The electrons and the split off hydrogen are transferred to cofactors such as NAD + or FAD .   

Different dehydrogenases can be distinguished depending on the substrate. For example, the enzyme that converts ethanol into acetaldehyde (ethanal) when alcohol is broken down in the liver is alcohol dehydrogenase ( EC ). The oxidation of L - lactate to pyruvate is catalyzed by lactate dehydrogenase ( EC ). Further representatives are glucose-6-phosphate dehydrogenase , glyceraldehyde-3-phosphate dehydrogenase , isocitrate dehydrogenase and malate dehydrogenase .   

Like all enzymes, dehydrogenases also catalyze the counter-reaction in reversible reactions, in this case the reduction . The counter-reaction to the above-mentioned oxidation of lactate to pyruvate is at least as important as this itself. It takes place during glycolysis when the pyruvate cannot be introduced into the citric acid cycle via acetyl-CoA and NAD + is required for other reactions, here especially for glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The enzyme involved in the reduction of pyruvate to lactate is in turn lactate dehydrogenase . Propanediol phosphate dehydrogenase has a similar substrate .

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